Controlling digital certificate use

ABSTRACT

A computing device includes a processor and a persistent memory for storing information about a first public key associated with a first asymmetric key pair for authenticating the source of a digital certificate. The computing device also includes a second memory for storing one or more current certificate version indicators, each associated with a corresponding digital certificate, and the version indicator is used by the processor to determine the trust of the corresponding digital certificate.

CROSS-REFERENCE TO RELATED APPLICATION

This application is related to U.S. patent application Ser. No.14/574,299, entitled “REDUCED OVERHEAD FOR CRYPTOGRAPHIC OPERATIONS,”filed Dec. 17, 2014, U.S. patent application Ser. No. 14/658,137,entitled “UPDATING ENCRYPTED CRYPTOGRAPHIC KEY,” filed Mar. 13, 2015,U.S. patent application Ser. No. 14/658,136, entitled “UPDATINGCRYPTOGRAPHIC KEY PAIR,” filed Mar. 13, 2015, and U.S. patentapplication Ser. No. 14/673,585, entitled “CONTROLLING USE OF ENCRYPTIONKEYS,” filed Mar. 30, 2015, now U.S. Pat. No. 9,479,340, commonly ownedand the contents of which are incorporated in their entirety byreference herein.

BACKGROUND

As an increasing amount of information is being transmitted and storedelectronically, and as the number of transactions performedelectronically through networks increases, there is an ever increasingneed to protect sensitive information in an electronic environment. Thisincludes not only securing the storing and transmitting of information,but also securing access to the information. A common approach is toencrypt information using an encryption algorithm or cipher to encodeinformation such that the information can only be decrypted or otherwiseinterpreted using a cryptographic key.

Digital certificates are often used to deliver public key values tosystems. These certificates and keys can be vulnerable to attacks andcan become compromised. Therefore, it is desirable to reduce thesecurity risks associated with updating digital certificates andcryptographic keys.

BRIEF DESCRIPTION OF THE DRAWINGS

Various embodiments in accordance with the present disclosure will bedescribed with reference to the drawings, in which:

FIG. 1 illustrates an exemplary architecture for features and systemsdescribed herein that includes one or more service provider computersand/or a user device connected via one or more networks, according to atleast one exemplary embodiment.

FIG. 2 illustrates cryptographic schemes using symmetric and asymmetrickeys according to one exemplary embodiment.

FIG. 3 illustrates a cryptographic scheme for generating andauthenticating a digital certificate using asymmetric keys according toone exemplary embodiment.

FIG. 4 illustrates contents of a digital certificate according to oneexemplary embodiment.

FIG. 5 illustrates a computing device including certificate and keyversion number checking according to one embodiment of the disclosedtechnologies.

FIG. 6 illustrates bit fields for storing certificate and key versionnumbers according to one exemplary embodiment.

FIG. 7A is a flowchart illustrating a method for authenticating adigital certificate including a certificate version number according toone embodiment of the disclosed technologies.

FIG. 7B is a flowchart illustrating a method for authenticating adigital certificate including a certificate version number according toanother embodiment of the disclosed technologies.

FIG. 7C is a flowchart illustrating a method for updating a certificateversion number according to an embodiment of the disclosed technologies.

FIG. 8A is a flowchart illustrating a method for authenticating acryptographic key including a key version number according to oneembodiment of the disclosed technologies.

FIG. 8B is a flowchart illustrating a method for authenticating acryptographic key including a key version number according to anotherembodiment of the disclosed technologies.

FIG. 8C is a flowchart illustrating a method for updating a key versionnumber according to an embodiment of the disclosed technologies.

FIG. 9A is a flowchart illustrating a method for authenticating acryptographic key including a key version number and no certificateversion number according to one embodiment of the disclosedtechnologies.

FIG. 9B is a flowchart illustrating a method for updating a key versionnumber according to an embodiment of the disclosed technologies.

FIG. 10 illustrates an encryption key provisioning system according toone embodiment of the disclosed technologies.

FIG. 11A is a flowchart illustrating a method for generating a digitalcertificate for delivering a cryptographic key including a certificateversion number and a key version number according to an embodiment ofthe disclosed technologies.

FIG. 11B is a flowchart illustrating a method for generating a digitalcertificate for delivering a cryptographic key including a key versionnumber according to an embodiment of the disclosed technologies.

FIG. 12 illustrates an environment in which various embodiments can beimplemented.

FIG. 13 illustrates an environment in which various embodiments can beimplemented.

DETAILED DESCRIPTION

In the following description, various embodiments will be described. Forpurposes of explanation, specific configurations and details are setforth in order to provide a thorough understanding of the embodiments.However, it will also be apparent to one skilled in the art that theembodiments may be practiced without the specific details. Furthermore,well-known features may be omitted or simplified in order not to obscurethe embodiment being described.

In a silicon product, secret cryptographic keys are often stored infuses on the device. In some devices, such as a processor or SoC(system-on-chip), each chip often has an asymmetric cryptographic keypair (including a private key and a public key) and a signed certificatefor performing cryptographic functions, and other device-specificinformation stored in fuses. The device can also have a root public keyfor secure communication with a provisioning server. The root public keyis considered to be trusted because it is burned into fuses in thedevice, or because it is integrated into the system boot ROM. In someapplications, a system may receive additional public keys that aredelivered with a trusted key certificate. Once the certificate has beenauthenticated, the system can trust items (e.g., certificates, firmwarebinaries) that can be authenticated with any public keys that may beincluded in extensions in that certificate.

Under certain circumstances, it may become desirable to replace thecryptographic keys in a computing device after the device has been inoperation. For example, the current key may have been compromised.Alternatively, certain preset limits may have been reached. For example,the number of cryptographic operations performed using the first privatekey may have reached a preset number, or the elapsed time of using thefirst private key may have reached a preset limit. In a scenario wherethe private key associated with one of the public keys is somehowcompromised, e.g., made public, the system vendor or the provisioningserver will need to generate a new key pair to replace the compromisedkey, and to generate and distribute a new trusted key certificate andassociated signed binaries and sub-certificates. However, this practicehas its limitations. For example, an attacker in possession of a copy ofthe old trusted key certificate can then sign any firmware binariesusing the compromised private key. Existing systems will still trustthose binaries as long as they are loaded along with the original(compromised) trusted key certificate. Therefore, there is a need for asecure method for updating cryptographic keys.

Embodiments of the disclosed technologies add a “version number”extension to the certificates loaded by a system. This version numbercorresponds to a value burned into firmware programmable fuses on thedevice. If the version in a given certificate is less than the valuestored in the corresponding fuses, the certificate will not be trustedby the system. If the version in a given certificate is equal to orhigher than the value stored in the corresponding fuses, the certificatewill be trusted by the system. In some embodiments, if the version in areceived certificate is greater than the value stored in the fuses, thefirmware will write a new value to the firmware programmable fuses, thuspreventing any certificates with lower version numbers from beingtrusted. The version update function can be controlled by a systemadministrator or another trusted entity. For example, in someembodiments, the version number is only updated with the authorizationfrom a system administrator or another trusted entity.

Some embodiments of the disclosed technologies also provide versionnumbers for specific keys in a similar manner. In this case, the trustedkey certificate will contain version numbers for each of the keys itincludes, and there will be corresponding fuses containing versionnumbers for each of the keys included in the system. Before trust isgranted to a given key, its version number is checked against theversion number in the fuses. In the above examples, version numbers areprovided to both the certificate and the key. In some embodiments, aversion number can be provided to either the digital certificate or thekey, but not both. Thus, embodiments of the disclosed technologiesprovide various methods and systems for replacing digital certificatesand cryptographic keys.

FIG. 1 illustrates an exemplary architecture for features and systemsdescribed herein that includes one or more service provider computersand/or a user device connected via one or more networks, according to atleast one exemplary embodiment. In architecture 100, one or more users102 may utilize user computing devices 104(1)-(N) (collectively, userdevices 104) to access applications provided by, e.g., a web browser ormobile device application, via one or more networks 108. In someaspects, these applications may be hosted, managed, and/or provided by acomputing resources service or service provider. One or more serviceprovider computers 110 may provide a native application which isconfigured to run on user devices 104 which user(s) 102 may interactwith.

As more information is being stored and more transactions are beingexecuted electronically through various networks, there is an everincreasing need for secure storing and transmitting of sensitiveinformation in an electronic environment. In addition, the devicesconnected to a network need to provide secure identity information andbe authenticated by the network. A common approach is to encryptinformation using an encryption algorithm or cipher to encodeinformation such that the information can only be decrypted or otherwiseinterpreted using cryptographic keys.

Modern semiconductor integrated circuit computing devices, e.g.,processors or SoCs, often are manufactured with device-specificinformation, such as device identification, stored in an on-chipnon-volatile memory, also referred to as persistent memory, such thatthe secure data are retained when the device power is turned off. Thesedevice-specific data are often stored in fuses that are burnt in a lateror final stage in device manufacturing. In security-sensitiveapplications where encryptions are desired, the information storedon-chip can include, for example, cryptographic keys and a digitalcertificate. Fuses or fuse-based memories are examples of immutablepersistent memories whose content cannot be altered. Other examples ofimmutable persistent memories can include read-only-memory (ROM).

Depending on the cryptographic algorithm, the cryptographic keys canrequire thousands of fuses, which can occupy significant die area in anintegrated circuit. Moreover, the fuse programming or burning processtends to be time-consuming and can increase the manufacturing cost ofthe device. Therefore, it is desirable to reduce the on-chip storage ofcryptographic information for a device. Embodiments of the disclosedtechnologies include techniques for storing a reduced number of bits onthe processor for performing cryptographic operations. According to someembodiments, two different cryptographic techniques are used to reducethe number of on-chip fuse bits in a device, as described in more detailbelow, with reference to FIG. 2.

In encryption, the message or information, referred to as plaintext, isencrypted using an encryption algorithm, generating a ciphertext, orencrypted message, that can only be read if decrypted. An encryptionscheme usually uses a pseudo-random encryption key generated by analgorithm. An authorized recipient can easily decrypt the message withthe key provided by the originator, but not unauthorized interceptors.In symmetric-key schemes, the encryption and decryption keys are thesame. Thus, communicating parties must have the same key before they canachieve secret communication. On the other hand, in public-keyencryption schemes, two keys are used: one for encryption and one fordecryption. For example, a private encryption key can be used to encryptmessages, which can only be read by receiving parties in possession of apublished decryption key. Alternatively, an encryption key can bepublished for multiple users to use and encrypt messages. However, onlythe receiving party has access to the decryption key that enablesencrypted messages to be read.

FIG. 2 illustrates cryptographic schemes using symmetric key andasymmetric keys, according to an exemplary embodiment. An example ofsymmetric key cryptography 200 is shown in FIG. 2, in which user A (210)and user B (220) both have the same secret key 201. In this example,user A (210) encrypts plain text 203 using key 201 in an encryptionprocess 204 to generate encrypted message 205. User A (210) then sendsencrypted message 205 to user B (220) using a transmission process 206.Upon receiving the encrypted message 205, user B decrypts it using thesame key 201 in a decryption process 207 to obtain the plain text 203.

In FIG. 2, an example of asymmetric key cryptography is shown as 250, inwhich user C (260) has both a private key 251 and a public key 252. Inthis example, user C can send the public key 252 to user D (270) using atransmission process 256. User C (260) encrypts a plain text 253 usingan encryption process 254 to generate an encrypted message 255. User Cthen sends encrypted message 255 to user D (270) using a transmissionprocess 257. In some cases, transmission processes 256 and 257 can bethe same process. Upon receiving the encrypted message 255, user Ddecrypts it using the public key 252 in a decryption process 257 toobtain the plain text 253.

There are many symmetric key cryptographic algorithms or schemes. TheAdvanced Encryption Standard (AES) is a symmetric block cipher ratifiedas a standard by National Institute of Standards and Technology (NIST)of the United States. AES is based on the Rijndael cipher, which uses adesign principle known as a substitution-permutation network, acombination of both substitution and permutation. The Rijndaelspecification is specified with block and key sizes that may be anymultiple of 32 bits, both with a minimum of 128 and a maximum of 256bits. The Rijndael algorithm involves several rounds of operation usinground keys derived from the cipher key using Rijndael's key schedule.The operations can include substitution, transposition, and mixing, etc.As described above, the same key is used in encryption as well asdecryption.

In contrast, in asymmetric key cryptography, different keys are used forencrypting and decrypting a message. In this case, one key can be madepublic while the other is kept secure. This arrangement is oftenreferred to as public key cryptography, and provides some distinctadvantages over symmetric encryption; for example, the necessity ofdistributing secret keys to large numbers of users is eliminated, andthe algorithm can be used for authentication as well as forcryptography. RSA (Rivest-Shamir-Adleman) is a public-key cryptosystemwidely used for secure data transmission. The algorithm is based onmathematical manipulation of two large prime numbers and their product.Its strength is believed to be related to the difficulty of factoring avery large prime number.

A method for generating public and private keys will be describedfurther below in connection with FIG. 6. In RSA, the public key consistsof the modulus n and the public (or encryption) exponent e. The privatekey consists of the modulus n and the private (or decryption) exponentd, which is kept secret. The process is explained using an example of apublic key holder sending an encrypted message to the private keyholder. The encryption of a message M is formed by computation using thefollowing formula,c≡m ^(e)(mod n)where m is an integer representation of the message M and 0≤m<n, (n, e)is the public key, mod is a modulus function, and c is the ciphertext.The decryption of ciphertext c is carried out by computation accordingto the following formula,m≡c ^(d)(mod n).where d is the private key exponent. The decrypted integerrepresentation m can be used to derive the original message M.

The security strength of the RSA scheme is related to its key size. Ithas been reported that to provide 128-bits of security forauthentication using RSA, it would need to have 3072 bits for theprivate key and over 1 kB (over 8000 bits) for the certificate. Thus, atotal of 12,000 or more bits would be necessary.

In the RSA algorithm, calculations are made modulo n, where n is aproduct of two large prime numbers p and q. 1,024-, 2,048- or 4,096-bitintegers n are commonly used, making calculations very time-consuming.By using the Chinese remainder theorem, however, parts of the privatekey can be pre-computed and stored, and the private key calculations inthe latter representation can be much faster.

Elliptic Curve Cryptography (ECC) is another public key scheme. Ingeneral, public-key cryptography is based on the intractability ofcertain mathematical problems. Early public-key systems, such as RSA,are secure assuming that it is difficult to factor a large integercomposed of two or more large prime factors. For elliptic-curve-basedprotocols, it is assumed that finding the discrete logarithm of a randomelliptic curve element with respect to a publicly known base point isinfeasible. The security of ECC depends on the ability to compute apoint multiplication and the inability to compute the multiplicand giventhe original and product points. The size of the elliptic curvedetermines the difficulty of the problem. The benefits offered by ECCare a smaller key size, reducing storage, and transmission requirements.For example, an elliptic curve group could provide the same level ofsecurity afforded by an RSA-based system with a large modulus andcorrespondingly larger key. For example, a 256-bit ECC public key hasbeen reported to provide comparable security to a 3072-bit RSA publickey. ECC can also offer faster private key operations, but public keyoperations can be slower than equivalent strength RSA.

In cryptography, a public key certificate (also known as a digitalcertificate or identity certificate, and will also be referred to as a“certificate” hereinafter) is an electronic document used to proveownership of a public key. The certificate includes information aboutthe key, information about its owner's identity, and the digitalsignature of an entity that has verified the certificate's contents arecorrect. In a typical public-key infrastructure (PKI) scheme, the signeris a certificate authority (CA). In other schemes, the signer can be thekey's owner. Certificates are an important component of Transport LayerSecurity (TLS, sometimes called by its older name SSL), where theyprevent an attacker from impersonating a secure website or other server.They are also used in other important applications, such as emailencryption and code signing. For example, when sending out encrypteddata, the sender often sends a digital certificate to distribute apublic key. In connecting to a network, a device needs to provide acertificate to the network such that the network can authenticate thedevice.

A digital signature is a mathematical scheme for demonstrating theauthenticity of a digital message or document. A valid digital signaturegives a recipient reason to believe that the message was created by aknown sender, such that the sender cannot deny having sent the message(authentication and non-repudiation) and that the message was notaltered in transit (integrity). Digital signatures often employ a typeof asymmetric cryptography. For messages sent through a non-securechannel, a properly implemented digital signature gives the receiverreason to believe the message was sent by the claimed sender. Digitallysigned messages or documents may be anything representable as a bitstring, including electronic mail, firmware binaries, or a message sentvia some other cryptographic protocol.

FIG. 3 illustrates a cryptographic scheme for signing and authenticatinga digital document using a digital certificate using asymmetric keysaccording to one exemplary embodiment. In FIG. 3, block 300 depicts thesteps user A (310) takes to prepare a digitally signed digital document319 including a message 313 for sending to user B (320). First, user Agenerates a private key 311 and a corresponding public key 312, using anasymmetric key generation algorithm, e.g., RSA. In an embodiment, adigital signature is an authentication mechanism that enables thecreator of a message to attach a code that acts as a signature. As shownin FIG. 3, user A performs a hash function 314 on message 313 to producea message digest 315. Next, user A encrypts message digest 315 usinguser A's private key 311 in an encryption process 316 to obtain anencrypted message digest 317, which is used as a digital signature. UserA then forms the signed document 319 that includes message 313, digitalsignature 317 which is the encrypted message digest, and user A'sdigital certificate 318. User A can send signed document 319 to user Busing a transmission process 340.

In FIG. 3, block 301 depicts the steps user B (320) takes toauthenticate a received digital document 329. After receiving digitaldocument 329, user B (320) uses the public key 312 contained in digitalcertificate 318 to decrypt the encrypted message digest 317 in adecryption process 326 to obtain a decrypted message digest 325. Basedon the information provided by digital certificate 318, user B alsoperforms hash function 314 on the received message 323 to obtain a newversion of message digest 327. User B then compares the new messagedigest 327 with the decrypted message digest 325 using a comparisonprocess 328. A match would indicate that decrypted message digest 325was encrypted using user A's private key, a proof that it was sent byuser A. Additionally, the matched message digests would indicate thatthe received message 323 is the same as the message 313 sent by user A.The integrity of the digital document can be established, and theauthentication process is completed.

FIG. 4 illustrates contents of a digital certificate according to anexemplary embodiment. As shown in FIG. 4, a digital certificate 400 is acertificate used to deliver a certificate version number, a new publickey, and a public key version number from a provisioning system to acomputing device. In an embodiment, certificate 400 can include thefollowing fields:

Field 401—Serial number to uniquely identify the certificate;

Field 402—Subject showing the person or entity identified;

Field 403—Validation date and expiration date of the certificate;

Field 404—Public key algorithm;

Field 405—Public key;

Field 406—Version number of the digital certificate;

Field 407—Secondary public key to be delivered;

Field 408—Version number of the secondary public key;

Field 409—Signature algorithm;

Field 410—Encrypted message digest of the certificate.

In the above example, some fields are used for identification purposes.For example, field 401 includes a serial number to uniquely identify thecertificate, and field 402 is a subject field showing the person orentity identified. In a certificate issued by a certificate authority(CA) to an entity, the subject field would show the identity and canalso include contact information of the entity. In the example of FIG.4, the certificate can be used to deliver a secondary public key orfirmware binaries to a computing device, and field 402 can includeidentity information of a provisioning system or server. Field 403includes a validation date and expiration date of the certificate, field404 includes the public key algorithm and field 405 is the public keyfor the recipient of the certificate to authenticate the certificate.The public key algorithm can be any asymmetric cryptographic algorithmthat the provisioning system has used to generate the asymmetric keypair. Field 406 can include a certificate version number of the digitalcertificate according to embodiments of the certificate. Field 407includes a secondary public key to be delivered and field 408 includes akey version number of the secondary public key according to embodimentsof the certificate. Field 409 includes the signature algorithm and field410 includes an encrypted message digest of the certificate. Thesignature algorithm (409) can include a hash algorithm for generatingthe message digest and an asymmetric algorithm, e.g., RSA, forencryption. The encrypted message digest (410) is sometimes referred toas the certificate signature. Fields 409 and 410 are used for thecomputing device receiving the certificate to authenticate thecertificate.

The above description of digital certificate 400 is merely an example ofa digital certificate that can be used in embodiments of the disclosedtechnologies. However, one skilled in the relevant art will appreciatethat the disclosed illustrative fields are not meant to be an exhaustiveidentification of all the fields required by or present in a certificate400. Rather, illustrative fields have been identified, in a non-limitingmanner, to facilitate illustration of one or more aspects of thedisclosed technologies. Further, various modifications or changes inlight thereof will be suggested to one skilled in the art. In someembodiments, digital certificate 400 is used for a provisioning serverto deliver public keys and firmware binaries to a computing device.Therefore, the content and format can be defined by the provisioningserver, and the firmware in the computing device is configured tointerpret the certificate. The certificate can also include otherinformation. For example, the certificate can also include the publickey algorithm associated with the secondary public key.

In some embodiments, the digital certificate can be configured accordingto the x.509 standard. In such embodiments, the certificate versionnumber associated with the digital certificate can be stored in anextension field in the digital certificate specified according to thex.509 standard. Similarly, the secondary public key and the key versionnumber associated with the secondary public key can also be stored in anextension field in the digital certificate specified according to thex.509 standard.

FIG. 5 illustrates a computing device configured to handle certificateand key version numbers checking according to one embodiment of thedisclosed technologies. However, one skilled in the relevant art willappreciate that the disclosed illustrative components are not meant tobe an exhaustive identification of all the components required by orpresent in a system 500. Rather, illustrative components have beenidentified, in a non-limiting manner, to facilitate illustration of oneor more aspects of the disclosed technologies. Still further, theillustrative components of system 500 can be considered logical innature such that the physical implementation of one or more componentscan be varied or such that one or more of the logical components may beimplemented in a virtualized manner. Additionally, one or more computingdevices can share one or more of the illustrated components, such asprocessors, graphical processing units, memory, and the like.

In an illustrative embodiment, system 500 is associated with varioushardware components, software components, and respective configurationsthat facilitate the implementation of security functions. For example,in one embodiment system 500 can include a computing device 510, e.g., asystem-on-chip (SoC), built in a single integrated circuit (IC) chip,for carrying out the operation of computing device 500. As shown in FIG.5, computing device 510 can have a processor (CPU) 511, a secondprocessor 512, and other processors 513, all coupled to a communicationchannel 515. In some embodiments, processor 511 and/or processor 512 canbe configured to perform security related functions, includingencryption, decryption, and authentication, etc., according to variousalgorithms. It is noted that in embodiments of the disclosedtechnologies, a security processor is optional, as security relatedfunctions can be implemented by other means, for example, by computercode executed by one or more processors, by hardware, or combinationsthereof. Computing device 510 can also have various memory units, suchas cache memory 517, a ROM (read-only memory) 518, and fuse-based memory550, also disposed on the same IC chip. In addition, computing device500 can have multiple peripheral devices, such as flash memory 520 on aseparate IC chip, other non-volatile storage devices 530, and otherperipheral devices 540. In some embodiments, SoC or computing device 510and flash memory 520 are separate IC chips disposed on the same systemcircuit board. The peripheral devices can include a networkcommunication interface 516 for establishing communication channelsbetween the computing device and one or more network based services orother computing devices, such as a cryptographic key provisioning system580 through network(s) 590. In some embodiments, the peripheral devicesmay be implemented using multiple discrete hardware elements, such asmultiple cards or other devices.

In FIG. 5, ROM 518, flash memory 520, and fuses 550 are examples ofnon-volatile memories, whereas ROM 518 and fuses 550 are an example ofan immutable persistent memory that cannot be altered. ROMs or mask ROMsare factory programmable (e.g., can be programmed during fabrication),and typically are used for large-volume products not required to beupdated after manufacture. For example, a boot ROM can include or locateboot loader software utilized to boot up system 500. In an embodiment,the ROM can include System Basic Input/Output System (SBIOS), which caninclude executable code, often referred to as firmware, that can beexecuted by one or more processors and used to cause components ofsystem 500 to initialize and identify system devices such as the videodisplay card, keyboard, mouse, hard disk drive, optical disc drive, andother hardware. In some embodiments, computing device 510 can alsoinclude firmware programmable fuses, an example of which is describedbelow with reference to FIG. 6.

Another type of non-volatile memory, programmable read-only memory(PROM), can be altered after manufacture, but requires specialprogrammer equipment, and data is stored by physically altering(burning) storage sites in the device. Yet another type of non-volatilememory, an electrically erasable programmable read-only memory (EEPROM),can be erased and programmed in-system. In FIG. 5, flash memory 520 mayinclude flash memory chips, which are a type of EEPROM that can onlyerase one block or “page” at a time. It is a solid-state chip thatmaintains stored data without any external power source. Flash memorydevices can offer high capacity and reasonable read/write speed, andmass production has lowered the cost of these commodity storage devices,making these chips a popular choice as secondary storage chips forprocessors.

Permanent device-specific information is often stored in a programmableread only memory (PROM) that can be programmed at a final test stage orin the system. Fuse-based PROMs can be programmed by electricallymelting conductive traces made of a metal or polysilicon material(blowing microscopic fuses) to cause a conductive path to be broken.Alternatively, some PROMs operate by sending a current to change theelectrical resistance of a material disposed between two conductors.

System 500 can also include additional components that are incommunication with one or more of the illustrative components associatedwith system 500. Such components can include one or more controllers incombination with one or more peripheral devices 540, such as hard disksor other storage devices.

According to some embodiments of the disclosed technologies, computingdevice 510 (also referred to as an SoC) in FIG. 5 can include apersistent memory, such as fuses 550 (also referred to as fuse-basedmemory) or ROM 518, for storing information about a first public key 551associated with a first asymmetric key pair, e.g. an RSA key pair. Insome embodiments, the first public key can be provisioned in thecomputing device in the manufacturing process by a provisioning server.This public key is also referred to as a root public key. This publickey is trusted by the system because it is burned into fuses in thedevice, or because it is integrated into the system boot ROM. Dependingon the embodiment, the information about the first public key can be thepublic key itself, or information that can be used to derive the publickey. The latter can include a hash of the public key that can be used toauthenticate a public key provided with a digital certificate. In anembodiment, the information about the first public key can include asymmetric key stored in the persistent memory that can be used todecrypt an encrypted public key stored in a flash memory. In yet anotherembodiment, the information about the first public key can include primenumbers stored in the persistent memory that can be used to derive anasymmetric key pair that includes the first public key. Further detailsof the information for deriving the first public key are described incommonly owned U.S. patent application Ser. No. 14/574,299, filed Dec.17, 2014, and U.S. patent application Ser. No. 14/658,137, filed Mar.13, 2015, the content of which is incorporated herein by reference.

In some embodiments, computing device 510 can also have a second memory.In an embodiment, the second memory can be a fuse-based memory, such asfuses 550 in FIG. 5. In other embodiments, the secondary memory can beanother memory, such as flash memory 520. The second memory is used forstoring one or more current certificate version indicators 552, eachassociated with a corresponding digital certificate. In someembodiments, the second memory is also configured for storing one ormore current key version indicators 553, each associated with acorresponding public key. Depending on the embodiment, this key can bethe root public key 551. In embodiments of the disclosed technology, theprocessor is further configured to perform cryptographic operationsusing the secondary public key with the current key version number.

FIG. 6 illustrates bit fields for storing certificate and key versionnumbers according to one exemplary embodiment. In system 500 illustratedin FIG. 5, each of the current certificate version numbers can be storedin a bit field in a fuse-based memory, in which the highest bit in thebit field with a value of “1” indicates the lowest certificate versionnumber to be trusted. Further, each of the current key version numberscan be stored in a bit field in the fuse-based memory, in which thehighest bit in the bit field with a value of “1” indicates the lowestkey version number to be trusted. As shown in FIG. 6, in bit field 610,since bit 15 is set, no version lower than 15 will be allowed to beloaded, and bits 14-0 will be ignored. If a new version isauthenticated, the bit field can be updated to reflect the change. Asshown in bit field 620, bit 16 is now set, and no version lower than 16will be allowed to be loaded. Bits 15-0 will be ignored.

In some embodiments, the fuse-based device used to store the versionnumbers can be firmware programmable fuses, such as the bit fielddescribed above, and the firmware can control the burning of the fuses.Alternatively, in other embodiments, the version numbers can be storedin a flash memory. In these cases, the version numbers can berepresented by binary numbers, and the version numbers can be updated bya counter and then stored in the flash memory.

In some embodiments, one of the processors in FIG. 5 can be configuredto perform a method of authenticating a digital certificate including acertificate version number as illustrated in the flowcharts in FIGS.7A-7C. In some embodiments, a processor can be further configured toperform a method for authenticating a cryptographic key including a keyversion number as illustrated in the flowcharts in FIGS. 8A-8C.

FIG. 7A is a flowchart illustrating a method 700 for authenticating adigital certificate including a certificate version number according toan embodiment of the disclosed technologies. Method 700 is summarizedbelow and explained with reference to FIGS. 4-6.

-   -   Process 701: Load a digital certificate with a certificate        version indicator;    -   Process 702: Authenticate the digital certificate;    -   Process 703: Compare the certificate version indicator with a        stored current version indicator;    -   Process 704: Determine the certificate is not a trusted        certificate, if the new version indicator is lower;    -   Process 705: Determine the certificate is a trusted certificate,        if the new version indicator is the same as the stored current        version indicator;    -   Process 706: Determine the certificate is a trusted certificate,        if the new version indicator is higher; and    -   Process 707: Update the stored current version indicator with        the new version indicator.

In some embodiments, method 700 illustrated in the flowchart in FIG. 7Acan be implemented using system 500 shown in FIG. 5. In an embodiment,method 700 can be carried out by computing device 510 in a secure bootprocess. For example, in process 701, processor 512 can be configured toload or read in a digital certificate from a memory, such as flashmemory 520. In some embodiments, the certificate may have been receivedfrom a provisioning server and stored in the memory. The certificate caninclude information as listed in FIG. 4, e.g., a certificate versionnumber and one or more secondary public keys, each with a correspondingkey version number. In process 702, processor 512 is configured toauthenticate the certificate. As illustrated in FIG. 3, theauthentication process can include decrypting an encrypted messagedigest and comparing it with the digest obtained by hashing the message.In some embodiments, the decryption is performed using the root publickey already stored in fuses 550. In process 703, after the certificateis authenticated, processor 512 is configured to compare the certificateversion indicator with the corresponding stored current certificateversion number in fuse-based memory 550 as illustrated in FIG. 5.Depending on the result of the comparison, processor 512 is configuredto perform different operations. For example, in process 704, if theversion indicator is lower than the stored current certificate versionindicator, the processor determines that the digital certificate is nota trusted certificate. In process 705, if the version indicator is equalto the stored current certificate version indicator, the processordetermines that the digital certificate is a trusted certificate. Inprocess 706, if the version indicator is higher than the stored currentcertificate version indicator, the processor determines that the digitalcertificate is a trusted certificate, and further, in process 707, theprocessor updates the corresponding stored current certificate versionindicator 551 in fuse-based memory 550 to reflect the new certificateversion indicator in the digital certificate. In embodiments in whichthe version indicator is stored in a bit field, the update operationincludes incrementing the version number by burning the next bit in thebit field.

FIG. 7B is a flowchart illustrating a method 750 for authenticating adigital certificate including a certificate version number according toan alternative embodiment of the disclosed technologies. Method 750 issummarized below.

-   -   Process 701: Load a digital certificate with a certificate        version indicator;    -   Process 702: Authenticate the digital certificate;    -   Process 703: Compare the version indicator with a stored current        version indicator;    -   Process 704: Determine the certificate is not a trusted        certificate, if the new version indicator is lower;    -   Process 705: Determine the certificate is a trusted certificate,        if the new version indicator is the same as the stored current        version indicator;    -   Process 706: Determine the certificate is a trusted certificate,        if the new version indicator is higher.

As shown above, method 750 is similar to method 700 outlined in theflowchart in FIG. 7A. Method 750 includes the same processes 701-706depicted in FIG. 7A. A difference is that in method 750, a higher newversion number of the trusted new certificate is not automaticallyupdated in the stored current version indicator. Method 750 allows thecurrent stored version number to remain valid, while a new version ofthe certificate can also being used.

As described above, methods 700 and 750 in FIGS. 7A and 7B illustrateoperations carried out by a computing device during a secure bootprocess to authenticate a digital certificate with an associated versionnumber. Depending on the embodiments, the stored current certificateversion number may or may not be updated, as illustrated in FIGS. 7A and7B, respectively. In method 750 shown in FIG. 7B, the version number isnot updated at boot up time, and multiple versions of the certificatecan be used. Subsequently, when the computing device is in operationafter boot up, if the system administrator or another trusted entitydetermines that a permanent change of the stored version number is inorder, the processor can then update the stored version indicator toreflect the new version number. For example, the version update may takeplace after the system administrator or another trusted entity decidesthat the new certificate is stable after a certain period of use.

FIG. 7C is a flowchart illustrating a method 780 for updating acertificate version number according to an embodiment of the disclosedtechnologies. In process 782 in FIG. 7C, the computing device checks tosee if a command or authorization has been received from a trustedentity to update the stored version number. The trusted entity caninclude a system administrator or other trusted entity, which hasdecided to update the version number. In process 784, if such a commandor authorization has been received, the computing device proceeds toupdate the stored version number. The version update operation issimilar to process 707 of method 700 described above in connection withFIG. 7A. If no command or authorization is received, then the storedversion number is not updated, and multiple versions of the certificatecan be considered trusted.

In some embodiments, after the certificate is determined to be a trustedcertificate, the processor is configured to further check the keyversion indicator of the secondary public key delivered by the digitalcertificate. FIG. 8A is a flowchart illustrating a method forauthenticating a cryptographic key including a key version numberaccording to one embodiment of the disclosed technologies. Method 800 issummarized below and explained with reference to FIGS. 4-6.

-   -   Process 801: Load a public key with a key version indicator;    -   Process 802: Authenticate the public key using the first public        key;    -   Process 803: Compare the key version indicator with a stored        current key version indicator;    -   Process 804: Determine the public key is not a trusted key, if        the new version indicator is lower;    -   Process 805: Determine the public key is a trusted key, if the        new version indicator is the same as the stored current version        indicator;    -   Process 806: Determine the public key is a trusted key, if the        new version indicator is higher; and    -   Process 807: Update the stored current key version indicator        with the new key version indicator.

Method 800 illustrated in the flowchart in FIG. 8A can be implementedusing the computing device shown in FIG. 5 in a secure boot process. Forexample, in process 801, processor 512 can be configured to load or readin a public key with an associated key version indicator that isdelivered with the digital certificate which has been authenticated. Inthis embodiment, the public key can be a secondary public key. Inprocess 802, processor 512 is configured to authenticate the key. Insome embodiments, the key may be authenticated in the same process forauthenticating the digital certificate, in which case process 802 can beoptionally skipped. In process 803, processor 512 is configured tocompare the key version indicator with the corresponding stored currentkey version indicator in fuse-based memory 550 as illustrated in FIG. 5.Depending on the result of the comparison, processor 512 is configuredto perform different operations. For example, in process 804, if theversion indicator is lower than the stored current key versionindicator, the processor determines that the key is not a trusted key.In process 805, if the version indicator is equal to the stored currentkey version indicator, the processor determines that the key is atrusted key. In process 806, if the version indicator is higher than thestored current certificate version indicator, the processor determinesthat the key is a trusted key, and further, in process 807, theprocessor updates the corresponding stored current key version indicator554 in fuse-based memory 550 with the new key version indicator in thedigital certificate. In some embodiments, the processor is furtherconfigured to store the secondary public key that has been determined asbeing trusted in the fuse-based memory.

FIG. 8B is a flowchart illustrating a method 850 for authenticating acryptographic key including a key version number according to anotherembodiment of the disclosed technologies. Method 850 is summarizedbelow.

-   -   Process 801: Load a public key with a key version indicator;    -   Process 802: Authenticate the public key using the first public        key;    -   Process 803: Compare the key version indicator with a stored        current key version indicator;    -   Process 804: Determine the public key is not a trusted key, if        the new version indicator is lower;    -   Process 805: Determine the public key is a trusted key, if the        new version indicator is the same as the stored current version        indicator;    -   Process 806: Determine the public key is a trusted key, if the        new version indicator is higher;

As shown above, method 850 is similar to method 800 outlined in theflowchart in FIG. 8A. For example, method 850 includes the sameprocesses 801-806 depicted in FIG. 8A. A difference is that, in method850, a higher new version number of the trusted new key is notautomatically updated in the stored current version indicator. Thus,method 850 allows the current stored version number to remain valid,while a new version of the key can also be used.

FIG. 8C is a flowchart illustrating a method 880 for updating a keyversion number according to an embodiment of the disclosed technologies.In process 882 in FIG. 8C, the computing device checks to see if acommand or authorization has been received from a trusted entity toupdate the stored version number. The trusted entity can include asystem administrator or other trusted entity, which has decided toupdate the version number. In process 884, if such a command orauthorization has been received, the computing device proceeds to updatethe stored version number. The version update operation is similar toprocess 807 of method 800 described above in connection with FIG. 8A. Ifno command or authorization is received, then the stored version numberis not updated, and multiple versions of the key can be consideredtrusted.

In the above descriptions, various memories are used for storing theversion numbers. In some embodiments, the persistent memory can be apersistent and immutable memory. In some embodiments, the persistentmemory is a fuse-based memory. In other embodiments, the persistentmemory is a system boot ROM (read only memory). In some embodiments, thesecond memory is a fuse-based memory. In some embodiments, the secondmemory is an electrically erasable programmable non-volatile memory.

In the above embodiments, a new certificate version number is providedwith the new digital certificate, and a new key version number isprovided with a new secondary public key. In some embodiments, a digitalcertificate with an associated certificate version number can be used todeliver a secondary public key without a key version number. In otherembodiments, a digital certificate without a certificate version numbercan be used to deliver a secondary public key without an associated akey version number.

FIG. 9A is a flowchart illustrating a method for authenticating acryptographic key including a key version number delivered by a digitalcertificate without a certificate version number according to anembodiment of the disclosed technologies. Method 900 is summarizedbelow.

-   -   Process 901: Load a digital certificate;    -   Process 902: Authenticate the digital certificate;    -   Process 903: Load a secondary public key with a key version        number;    -   Process 904: Authenticate the public key;    -   Process 905: Compare the key version indicator with a stored        current version indicator;    -   Process 906: Determine the key is not a trusted certificate, if        the new version indicator is lower;    -   Process 907: Determine the certificate is a trusted certificate,        if the new version indicator is the same as the stored current        version indicator;    -   Process 908: Determine the certificate is a trusted certificate,        if the new version indicator is higher; and    -   Process 909: Optionally, update the stored current version        indicator with the new version indicator.

In some embodiments, method 900 illustrated in the flowchart in FIG. 9Acan be implemented using system 500 shown in FIG. 5. In an embodiment,method 900 can be carried out by computing device 510 in a secure bootprocess. In processes 901 and 902, a digital certificate is loaded andauthenticated. These processes are similar to processes 701 and 702 ofmethod 700 described above for loading and authenticating a digitalcertificate. In processes 903-908, the processor to authenticate thesecondary public key delivered by the digital certificate and check thekey version number. Processes 903-908 are similar to processes 801-806in method 800 described above in connection with FIG. 8A. In method 900,process 909 is an optional process, shown in dotted box in FIG. 9A, ofupdating the stored key version number. In some embodiments, if theversion indicator is higher than the stored current certificate versionindicator and the processor determines that the key is a trusted key,the processor updates the corresponding stored current key versionindicator in fuse-based memory with the new key version indicator in thedigital certificate, similar to process 807 of method 800 in FIG. 8A. Insome embodiments, the stored key version number is not updated duringthe secure boot process, similar to method 850 in FIG. 8B. In this case,the system allows the current stored version number to remain valid,while a new version of the key can also be used.

FIG. 9B is a flowchart illustrating a method 980 for updating a keyversion number according to an embodiment of the disclosed technologies.As shown in FIG. 9B, method 980 is similar to method 880 shown in FIG.8C. In FIG. 9B, in process 982, the processor in the computing devicechecks to see if a command or authorization has been received from atrusted entity to update the stored version number. The trusted entitycan include a system administrator or other trusted entity, which hasdecided to update the version number. In process 984, if such a commandor authorization has been received, the computing device proceeds toupdate the stored version number. The version update operation issimilar to process 807 of method 800 described above in connection withFIG. 8A. If no command or authorization is received, then the storedversion number is not updated, and multiple versions of the key can beconsidered trusted.

FIG. 10 illustrates a cryptographic key provisioning system according toan embodiment of the disclosed technologies. In FIG. 10, keyprovisioning system 1000 includes a key generation and provisioningsystem 1010, programming equipment 1020, and a device 1030 for receivingkey provisioning. Key generation and provisioning system 1010 caninclude a key generation unit 1012, which is configured to generate keysfor symmetric and asymmetric cryptography, using known methods. Keygeneration and provisioning system 1010 can also include a keyprovisioning unit 1014, which is configured to manage key provisioningactivities. In some embodiments, programming equipment 1020 can includea fuse programmer 1022 and a flash programmer 1024, which are used toprogram the keys generated by the key generation and provisioning system1010 into a device 1030. As shown in FIG. 10, device 1030 can include acomputing device or system-on-chip 1040, which can have a processor 1042and fuses block 1044. Device 1030 can also have a flash memory 1050disposed in a second IC chip. For example, device 1030 can representsystem 500 in FIG. 5. Key provisioning system 1000 can be configured toimplement the various functions. For example, these functions includegenerating a private key and a public key for an asymmetriccryptographic algorithm, generating a symmetric key for a symmetriccryptographic algorithm, and encrypting the private key using thesymmetric key. The functions also include programming a first memory ofa computing device with the symmetric key, and programming a secondmemory with the encrypted private key. These functions also includegenerating prime numbers or other reduced set of information and programthe prime numbers or reduced set of information into a first memory in acomputing device to be used for the computing device to derivecryptographic keys.

In addition, as shown in FIG. 10, key provisioning system 1000 can alsoinclude components for providing key updating capabilities. In certaininstances, the key provisioning system 1000 may detect trigger eventsfor updating the keys for one or more devices. Trigger events mayinclude elapsing of time, completion of a number of transactions by adevice, or a potential security compromise in the device or theinfrastructure supporting the device, etc. To support the key updatingfunctions, key generation and provisioning system 1010 can include anetwork interface 1019 for communicating with device 1030 throughnetwork(s) 1080. Device 1030 also can have a network interface 1060 forcommunicating with network 1080. Further, key generation andprovisioning system 1010 also includes processor(s) 1016 and memories1018. In various embodiments, the key provisioning system can beconfigured to provide key provisioning functions for the variouscomputing devices described above. The programming equipment 1020 in keyprovisioning system 1000 is shown in broken lines to indicate that thekey updating functions performed through network(s) 1080 can be carriedout by a key provisioning system or server separate from the keyprovisioning system that includes the programming equipment. The variouskey provisioning functions are described below with reference to theflowchart illustrated in FIG. 11A.

FIG. 11A is a flowchart illustrating a method 1100 for generating adigital certificate for delivering a cryptographic key including a keyversion number according to one embodiment of the disclosedtechnologies.

According to some embodiments of the disclosed technologies, a method1100 is provided for a key provisioning system to deliver acryptographic key to a computing device. The computing device has afirst public key associated with a first asymmetric key pair. The methodis summarized in the flowchart illustrated in FIG. 11A and outlinedbelow.

-   -   Process 1102: Generate a new secondary public key and key        version number;    -   Process 1104: Generate a digital certificate with a certificate        version number including the first public key for authentication        and the new secondary public key and key version number;    -   Process 1106: Sign the digital certificate using first private        key associated with the first public key;    -   Process 1108: Send the digital certificate to the computing        device.

In an embodiment, the key provisioning method can be implemented usingthe key provisioning system 1100 illustrated in FIG. 10. For example, inprocess 1102, key provisioning system 900 is configured to generate asecondary public key associated with a second asymmetric key pair and acorresponding key version number. In an embodiment, the secondasymmetric key pair can be an RSA key pair or an ECC key pair, or othersuitable asymmetric key pair. In process 1104, key provisioning system1000 is configured to generate a digital certificate. In someembodiments, key provisioning system 1000 is also configured to generatea certificate version number associated with the digital certificate.The certificate also includes a corresponding certificate version numberand the first public key for the computing device to authenticate thedigital certificate. The digital certificate further includes thesecondary public key and the corresponding key version number associatedwith the second public key to be delivered to the computing device. Insome embodiments, the certificate version number associated with thedigital certificate is higher than a certificate version number sentpreviously to the computing device, and the key version numberassociated with the secondary public key is higher than a public keyversion number sent previously to the computing device. In process 1106,as described above in connection with FIGS. 4-8, key provisioning system900 is configured to sign the digital certificate. In some embodiments,the signing process can include using a hash algorithm to generate amessage digest of a portion of the digital certificate, encrypting themessage digest using a first private key associated with the firstasymmetric key pair, and including the encrypted message digest in thedigital certificate. In process 1108, key provisioning system 1000 isconfigured to send the digital certificate to the computing device. Asdescribed above in connection with FIGS. 4-9B, this digital certificatehas the content to allow the computing device to authenticate thedigital certificate using the first public key and the certificateversion number. Further, after determining the digital certificate to bea trusted certificate, the computing device can extract the secondpublic key and the key version number from the digital certificate. Inembodiments of the disclosed technologies, the computing device isconfigured to authenticate the digital certificate and check thecertificate version number to determine whether the digital certificateis considered a trusted certificate. The computing device is furtherconfigured to use the key version number to verify whether the secondpublic key can be considered a trusted public key. Depending on theembodiments, the new secondary public key can be used to replace asecondary public key previously sent to the computing device.

In the above embodiment, a new certificate version number is providedwith the new digital certificate, and a new key version number isprovided with a new secondary public key. In some embodiments, a digitalcertificate with an associated certificate version number can be used todeliver a secondary public key without a key version number. In otherembodiments, a digital certificate without a certificate version numbercan be used to deliver a secondary public key without an associated akey version number.

FIG. 11B is a flowchart illustrating a method 1150 for generating adigital certificate for delivering a cryptographic key including a keyversion number according to an embodiment of the disclosed technologies.In this embodiment, the computing device has a first public keyassociated with a first asymmetric key pair. The method is summarized inthe flowchart illustrated in FIG. 11B and outlined below.

-   -   Process 1152: Generate a new secondary public key and key        version number;    -   Process 1154: Generate a digital certificate including the first        public key for authentication and the new secondary public key        and key version number;    -   Process 1156: Sign the digital certificate using first private        key associated with the first public key; and    -   Process 1158: Send the digital certificate to the computing        device.

As shown in FIG. 11B, method 1150 is similar to method 1100 in FIG. 11Adescribed above. A difference is that, in process 1154, no certificateversion number is generated with the digital certificate. In this case,the computing device receiving the certificate will check the versionnumber of the secondary public key delivered by the certificate withoutchecking the version number of the certificate, using methodsillustrated in FIGS. 9A and 9B.

The processes described herein, or variations and/or combinationsthereof, may be performed under the control of one or more computersystems configured with executable instructions and may be implementedas code (e.g., executable instructions, one or more computer programs orone or more applications) executing collectively on one or moreprocessors, by hardware or combinations thereof. The code may be storedon a computer-readable storage medium, for example, in the form of acomputer program comprising a plurality of instructions executable byone or more processors. The computer-readable storage medium may benon-transitory.

FIG. 12 illustrates an exemplary architecture for features and systemsdescribed herein that includes one or more service provider computersand/or a user device connected via one or more networks, according to atleast one exemplary embodiment. The devices discussed in FIGS. 1-11 mayuse one or more components of the computing devices described in FIG. 12or may represent one or more computing devices described in FIG. 12. Inarchitecture 1200, one or more users 1202 may utilize user computingdevices 1204(1)-(N) (collectively, user devices 1204) to accessapplication 1206 (e.g., a web browser or mobile device application), viaone or more networks 12011. In some aspects, application 1206 may behosted, managed, and/or provided by a computing resources service orservice provider. One or more service provider computers 1210 mayprovide a native application which is configured to run on user devices1204 which user(s) 1202 may interact with. Service provider computer(s)1210 may, in some examples, provide computing resources such as, but notlimited to, client entities, low latency data storage, durable datastorage, data access, management, virtualization, cloud-based softwaresolutions, electronic content performance management, etc. Serviceprovider computer(s) 1210 may also be operable to provide web hosting,computer application development and/or implementation platforms,combinations of the foregoing or the like to user(s) 1202. Serviceprovider computer(s) 1210, in some examples, may communicate with one ormore third party computers 1212.

In some examples, network(s) 1208 may include any one or a combinationof many different types of networks, such as cable networks, theInternet, wireless networks, cellular networks and other private and/orpublic networks. While the illustrated example represents user(s) 1202accessing application 1206 over network(s) 1208, the describedtechniques may equally apply in instances where user(s) 1202 interactwith service provider computer(s) 1210 via user device(s) 1204 over alandline phone, via a kiosk or in any other manner. It is also notedthat the described techniques may apply in other client/serverarrangements (e.g., set-top boxes, etc.), as well as innon-client/server arrangements (e.g., locally stored applications,etc.).

As described briefly above, application 1206 may allow user(s) 1202 tointeract with service provider computer(s) 1210 such as to access webcontent (e.g., web pages, music, video, etc.). Service providercomputer(s) 1210, perhaps arranged in a cluster of servers or as aserver farm, may host application 1206 and/or cloud-based softwareservices. Other server architectures may also be used to hostapplication 1206. Application 1206 may be capable of handling requestsfrom many users 1202 and serving, in response, various item web pages.Application 1206 can provide any type of website that supports userinteraction, including social networking sites, online retailers,informational sites, blog sites, search engine sites, news andentertainment sites, and so forth. As discussed above, the describedtechniques can similarly be implemented outside of application 1206,such as with other applications running on user device(s) 1204.

User device(s) 1204 may be any type of computing device such as, but notlimited to, a mobile phone, a smart phone, a personal digital assistant(PDA), a laptop computer, a desktop computer, a thin-client device, atablet PC, an electronic book (e-book) reader, etc. In some examples,user device(s) 1204 may be in communication with service providercomputer(s) 1210 via network(s) 1208, or via other network connections.Additionally, user device(s) 1204 may be part of the distributed systemmanaged by, controlled by or otherwise part of service providercomputer(s) 1210 (e.g., a console device integrated with serviceprovider computers 1210).

In one illustrative configuration, user device(s) 1204 may include atleast one memory 1214 and one or more processing units (or processor(s))1216. Processor(s) 1216 may be implemented as appropriate in hardware,computer-executable instructions, firmware, or combinations thereof.Computer-executable instruction or firmware implementations ofprocessor(s) 1216 may include computer-executable or machine-executableinstructions written in any suitable programming language to perform thevarious functions described. User device(s) 1204 may also includegeo-location devices (e.g., a global positioning system (GPS) device orthe like) for providing and/or recording geographic location informationassociated with user device(s) 1204.

Memory 1214 may store program instructions that are loadable andexecutable on processor(s) 1216, as well as data generated during theexecution of these programs. Depending on the configuration and type ofuser device(s) 1204, memory 1214 may be volatile (such as random accessmemory (RAM)) and/or non-volatile (such as read-only memory (ROM), flashmemory, etc.). User device(s) 1204 may also include additional removablestorage and/or non-removable storage including, but not limited to,magnetic storage, optical disks and/or tape storage. The disk drives andtheir associated computer-readable media may provide non-volatilestorage of computer-readable instructions, data structures, programmodules, and other data for the computing devices. In someimplementations, memory 1214 may include multiple different types ofmemory, such as static random access memory (SRAM), dynamic randomaccess memory (DRAM), or ROM.

Turning to the contents of memory 1214 in more detail, memory 1214 mayinclude an operating system and one or more application programs orservices for implementing the features disclosed herein including atleast a user provided input element or electronic service web page, suchas via browser application 1206 or dedicated applications (e.g., smartphone applications, tablet applications, etc.). Browser application 1206may be configured to receive, store and/or display a website or otherinterface for interacting with service provider computer(s) 1210.Additionally, memory 1214 may store access credentials and/or other userinformation such as, but not limited to, user IDs, passwords, and/orother user information. In some examples, the user information mayinclude information for authenticating an account access request suchas, but not limited to, a device ID, a cookie, an IP address, alocation, or the like. In addition, the user information may include auser-provided response to a security question or a geographic locationobtained by the user device 1204.

In some aspects, service provider computer(s) 1210 may also be any typeof computing devices such as, but not limited to, a mobile phone, asmart phone, a personal digital assistant (PDA), a laptop computer, adesktop computer, a server computer, a thin-client device, a tablet PC,etc. Additionally, it should be noted that in some embodiments, serviceprovider computer(s) 1210 are executed by one or more virtual machinesimplemented in a hosted computing environment. The hosted computingenvironment may include one or more rapidly provisioned and releasedcomputing resources, which computing resources may include computing,networking and/or storage devices. A hosted computing environment mayalso be referred to as a cloud computing environment. In some examples,service provider computer(s) 1210 may be in communication with userdevice(s) 1204 and/or other service providers via network(s) 1208, orvia other network connections. Service provider computer(s) 1210 mayinclude one or more servers, perhaps arranged in a cluster, as a serverfarm, or as individual servers not associated with one another. Theseservers may be configured to implement the keyword classification andrating feature services described herein as part of an integrated,distributed computing environment.

In one illustrative configuration, service provider computer(s) 1210 mayinclude at least one memory 1218 and one or more processing units (orprocessor(s)) 1220. Processor(s) 1220 may be implemented as appropriatein hardware, computer-executable instructions, firmware, or combinationsthereof. Computer-executable instruction or firmware implementations ofprocessor(s) 1220 may include computer-executable or machine-executableinstructions written in any suitable programming language to perform thevarious functions described.

In some instances, hardware processor(s) 1220 may be a single coreprocessor or a multi-core processor. A multi-core processor may includemultiple processing units within the same processor. In someembodiments, the multi-core processors may share certain resources, suchas busses and second or third level of cache between multiple-cores. Insome instances, each core in a single or multi-core processor may alsoinclude multiple executing logical processors (or threads). In such acore (that supports multiple logical processors), several stages of theexecution pipeline and also lower level caches may also be shared.

Memory 1218 may store program instructions that are loadable andexecutable on processor(s) 1220, as well as data generated during theexecution of these programs. Depending on the configuration and type ofservice provider computer(s) 1210, memory 1218 may be volatile (such asRAM) and/or non-volatile (such as ROM, flash memory, etc.). Serviceprovider computer(s) 1210 or servers may also include additional storage1222, which may include removable storage and/or non-removable storage.The additional storage 1222 may include, but is not limited to, magneticstorage, optical disks and/or tape storage. The disk drives and theirassociated computer-readable media may provide non-volatile storage ofcomputer-readable instructions, data structures, program modules, andother data for the computing devices. In some implementations, memory1218 may include multiple different types of memory, such as SRAM, DRAM,or ROM.

Memory 1218, the additional storage 1222, both removable andnon-removable are all examples of computer-readable storage media. Forexample, computer-readable storage media may include volatile ornon-volatile, removable or non-removable media implemented in any methodor technology for storage of information such as computer-readableinstructions, data structures, program modules, or other data. Memory1218 and the additional storage 1222 are all examples of computerstorage media. Additional types of computer storage media that may bepresent in service provider computer(s) 1210 may include, but are notlimited to, PRAM, SRAM, DRAM, RAM, ROM, EEPROM, flash memory or othermemory technology, CD-ROM, DVD or other optical storage, magneticcassettes, magnetic tape, magnetic disk storage or other magneticstorage devices, or any other medium which can be used to store thedesired information and which can be accessed by service providercomputer(s) 1210. Combinations of any of the above should also beincluded within the scope of computer-readable media.

Alternatively, computer-readable communication media may includecomputer-readable instructions, program modules or other datatransmitted within a data signal, such as a carrier wave or othertransmission. However, as used herein, computer-readable storage mediadoes not include computer-readable communication media.

Service provider computer(s) 1210 may also contain communicationsconnection(s) 1224 that allow service provider computer(s) 1210 tocommunicate with a stored database, another computing device or server,user terminals and/or other devices on network(s) 1208. Service providercomputer(s) 1210 may also include I/O device(s) 826, such as a keyboard,a mouse, a pen, a voice input device, a touch input device, a display,speakers, a printer, and the like.

Memory 1218 may include an operating system 1228, one or more datastores 1230 and/or one or more application programs or services forimplementing the features disclosed herein, including a managementbuffer 1232 and a logging buffer 1240. The modules described herein maybe software modules, hardware modules or a suitable combination thereof.If the modules are software modules, the modules can be embodied on anon-transitory computer readable medium and processed by a processor inany of the computer systems described herein. It should be noted thatthe described processes and architectures can be performed either inreal-time or in an asynchronous mode prior to any user interaction. Themodules may be configured in the manner suggested in FIG. 12, and/orfunctions described herein can be provided by one or more modules thatexist as separate modules and/or module functions described herein canbe spread over multiple modules.

FIG. 13 illustrates aspects of an example environment 1300 forimplementing aspects in accordance with various embodiments. As will beappreciated, although a Web-based environment is used for purposes ofexplanation, different environments may be used, as appropriate, toimplement various embodiments. The environment includes an electronicclient device 1302, which can include any appropriate device operable tosend and receive requests, messages, or information over an appropriatenetwork 1304 and convey information back to a user of the device.Examples of such client devices include personal computers, cell phones,handheld messaging devices, laptop computers, set-top boxes, personaldata assistants, electronic book readers, and the like. The network caninclude any appropriate network, including an intranet, the Internet, acellular network, a local area network or any other such network orcombination thereof. Components used for such a system can depend atleast in part upon the type of network and/or environment selected.Protocols and components for communicating via such a network are wellknown and will not be discussed herein in detail. Communication over thenetwork can be enabled by wired or wireless connections and combinationsthereof. In this example, the network includes the Internet, as theenvironment includes a Web server 1306 for receiving requests andserving content in response thereto, although for other networks analternative device serving a similar purpose could be used as would beapparent to one of ordinary skill in the art.

The illustrative environment includes at least one application server1308 and a data store 1310. It should be understood that there can beseveral application servers, layers, or other elements, processes orcomponents, which may be chained or otherwise configured, which caninteract to perform tasks such as obtaining data from an appropriatedata store. As used herein the term “data store” refers to any device orcombination of devices capable of storing, accessing and retrievingdata, which may include any combination and number of data servers,databases, data storage devices and data storage media, in any standard,distributed or clustered environment. The application server can includeany appropriate hardware and software for integrating with the datastore as needed to execute aspects of one or more applications for theclient device, handling a majority of the data access and business logicfor an application. The application server provides access controlservices in cooperation with the data store and is able to generatecontent such as text, graphics, audio and/or video to be transferred tothe user, which may be served to the user by the Web server in the formof HyperText Markup Language (“HTML”), Extensible Markup Language(“XML”) or another appropriate structured language in this example. Thehandling of all requests and responses, as well as the delivery ofcontent between the client device 1302 and the application server 1308,can be handled by the Web server. It should be understood that the Weband application servers are not required and are merely examplecomponents, as structured code discussed herein can be executed on anyappropriate device or host machine as discussed elsewhere herein.

The data store 1310 can include several separate data tables, databasesor other data storage mechanisms and media for storing data relating toa particular aspect. For example, the data store illustrated includesmechanisms for storing production data 1313 and user information 1316,which can be used to serve content for the production side. The datastore also is shown to include a mechanism for storing log data 1314,which can be used for reporting, analysis, or other such purposes. Itshould be understood that there can be many other aspects that may needto be stored in the data store, such as for page image information andto access right information, which can be stored in any of the abovelisted mechanisms as appropriate or in additional mechanisms in the datastore 1310. The data store 1310 is operable, through logic associatedtherewith, to receive instructions from the application server 1308 andobtain, update or otherwise process data in response thereto. In oneexample, a user might submit a search request for a certain type ofitem. In this case, the data store might access the user information toverify the identity of the user and can access the catalog detailinformation to obtain information about items of that type. Theinformation then can be returned to the user, such as in a resultslisting on a Web page that the user is able to view via a browser on theuser device 1302. Information for a particular item of interest can beviewed in a dedicated page or window of the browser.

Each server typically will include an operating system that providesexecutable program instructions for the general administration andoperation of that server and typically will include a computer-readablestorage medium (e.g., a hard disk, random access memory, read onlymemory, etc.) storing instructions that, when executed by a processor ofthe server, allow the server to perform its intended functions. Suitableimplementations for the operating system and general functionality ofthe servers are known or commercially available and are readilyimplemented by persons having ordinary skill in the art, particularly inlight of the disclosure herein.

The environment in one embodiment is a distributed computing environmentutilizing several computer systems and components that areinterconnected via communication links, using one or more computernetworks or direct connections. However, it will be appreciated by thoseof ordinary skill in the art that such a system could operate equallywell in a system having fewer or a greater number of components than areillustrated in FIG. 13. Thus, the depiction of the system 1300 in FIG.13 should be taken as being illustrative in nature and not limiting tothe scope of the disclosure.

The various embodiments further can be implemented in a wide variety ofoperating environments, which in some cases can include one or more usercomputers, computing devices or processing devices which can be used tooperate any of a number of applications. User or client devices caninclude any of a number of general purpose personal computers, such asdesktop or laptop computers running a standard operating system, as wellas cellular, wireless and handheld devices running mobile software andcapable of supporting a number of networking and messaging protocols.Such a system also can include a number of workstations running any of avariety of commercially-available operating systems and other knownapplications for purposes such as development and database management.These devices also can include other electronic devices, such as dummyterminals, thin-clients, gaming systems and other devices capable ofcommunicating via a network.

Most embodiments utilize at least one network that would be familiar tothose skilled in the art for supporting communications using any of avariety of commercially-available protocols, such as TransmissionControl Protocol/Internet Protocol (“TCP/IP”), Open SystemInterconnection (“OSI”), File Transfer Protocol (“FTP”), Universal Plugand Play (“UpnP”), Network File System (“NFS”), Common Internet FileSystem (“CIFS”) and AppleTalk. The network can be, for example, a localarea network, a wide-area network, a virtual private network, theInternet, an intranet, an extranet, a public switched telephone network,an infrared network, a wireless network and any combination thereof.

In embodiments utilizing a Web server, the Web server can run any of avariety of server or mid-tier applications, including Hypertext TransferProtocol (“HTTP”) servers, FTP servers, Common Gateway Interface (“CGI”)servers, data servers, Java servers and business application servers.The server(s) also may be capable of executing programs or scripts inresponse requests from user devices, such as by executing one or moreWeb applications that may be implemented as one or more scripts orprograms written in any programming language, such as Java®, C, C# orC++, or any scripting language, such as Perl, Python or TCL, as well ascombinations thereof. The server(s) may also include database servers,including without limitation those commercially available from Oracle®,Microsoft®, Sybase®, and IBM®.

The environment can include a variety of data stores and other memoryand storage media as discussed above. These can reside in a variety oflocations, such as on a storage medium local to (and/or resident in) oneor more of the computers or remote from any or all of the computersacross the network. In a particular set of embodiments, the informationmay reside in a storage-area network (“SAN”) familiar to those skilledin the art. Similarly, any necessary files for performing the functionsattributed to the computers, servers or other network devices may bestored locally and/or remotely, as appropriate. Where a system includescomputerized devices, each such device can include hardware elementsthat may be electrically coupled via a bus, the elements including, forexample, at least one central processing unit (“CPU”), at least oneinput device (e.g., a mouse, keyboard, controller, touch screen orkeypad) and at least one output device (e.g., a display device, printeror speaker). Such a system may also include one or more storage devices,such as disk drives, optical storage devices and solid-state storagedevices such as random access memory (“RAM”) or read-only memory(“ROM”), as well as removable media devices, memory cards, flash cards,etc.

Such devices also can include a computer-readable storage media reader,a communications device (e.g., a modem, a network card (wireless orwired), an infrared communication device, etc.) and working memory asdescribed above. The computer-readable storage media reader can beconnected with, or configured to receive, a computer-readable storagemedium, representing remote, local, fixed, and/or removable storagedevices as well as storage media for temporarily and/or more permanentlycontaining, storing, transmitting and retrieving computer-readableinformation. The system and various devices also typically will includea number of software applications, modules, services or other elementslocated within at least one working memory device, including anoperating system and application programs, such as a client applicationor Web browser. It should be appreciated that alternate embodiments mayhave numerous variations from that described above. For example,customized hardware might also be used and/or particular elements mightbe implemented in hardware, software (including portable software, suchas applets) or both. Further, connection to other computing devices suchas network input/output devices may be employed.

Storage media and computer readable media for containing code, orportions of code, can include any appropriate media known or used in theart, including storage media and communication media, such as but notlimited to volatile and non-volatile, removable and non-removable mediaimplemented in any method or technology for storage and/or transmissionof information such as computer readable instructions, data structures,program modules or other data, including RAM, ROM, Electrically ErasableProgrammable Read-Only Memory (“EEPROM”), flash memory or other memorytechnology, Compact Disc Read-Only Memory (“CD-ROM”), digital versatiledisk (DVD) or other optical storage, magnetic cassettes, magnetic tape,magnetic disk storage or other magnetic storage devices or any othermedium which can be used to store the desired information and which canbe accessed by the a system device. Based on the disclosure andteachings provided herein, a person of ordinary skill in the art willappreciate other ways and/or methods to implement the variousembodiments.

The specification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense. It will, however, beevident that various modifications and changes may be made thereuntowithout departing from the broader spirit and scope of the disclosure asset forth in the claims.

Other variations are within the spirit of the present disclosure. Thus,while the disclosed techniques are susceptible to various modificationsand alternative constructions, certain illustrated embodiments thereofare shown in the drawings and have been described above in detail. Itshould be understood, however, that there is no intention to limit thedisclosure to the specific form or forms disclosed, but on the contrary,the intention is to cover all modifications, alternative constructionsand equivalents falling within the spirit and scope of the disclosure,as defined in the appended claims.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the disclosed embodiments (especially in thecontext of the following claims) are to be construed to cover both thesingular and the plural, unless otherwise indicated herein or clearlycontradicted by context. The terms “comprising,” “having,” “including,”and “containing” are to be construed as open-ended terms (i.e., meaning“including, but not limited to,”) unless otherwise noted. The term“connected” is to be construed as partly or wholly contained within,attached to, or joined together, even if there is something intervening.Recitation of ranges of values herein are merely intended to serve as ashorthand method of referring individually to each separate valuefalling within the range, unless otherwise indicated herein and eachseparate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate embodiments of the disclosure anddoes not pose a limitation on the scope of the disclosure unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe disclosure.

Disjunctive language such as the phrase “at least one of X, Y, or Z,”unless specifically stated otherwise, is intended to be understoodwithin the context as used in general to present that an item, term,etc., may be either X, Y, or Z, or any combination thereof (e.g., X, Y,and/or Z). Thus, such disjunctive language is not generally intended to,and should not, imply that certain embodiments require at least one ofX, at least one of Y, or at least one of Z to each be present.

Various embodiments of this disclosure are described herein, includingthe best mode known to the inventors for carrying out the disclosure.Variations of those embodiments may become apparent to those of ordinaryskill in the art upon reading the foregoing description. The inventorsexpect skilled artisans to employ such variations as appropriate and theinventors intend for the disclosure to be practiced otherwise than asspecifically described herein. Accordingly, this disclosure includes allmodifications and equivalents of the subject matter recited in theclaims appended hereto as permitted by applicable law. Moreover, anycombination of the above-described elements in all possible variationsthereof is encompassed by the disclosure unless otherwise indicatedherein or otherwise clearly contradicted by context.

All references, including publications, patent applications and patents,cited herein are hereby incorporated by reference to the same extent asif each reference were individually and specifically indicated to beincorporated by reference and were set forth in its entirety herein.

What is claimed is:
 1. A system-on-chip, comprising: a processor; and afuse-based memory storing: information for deriving a first public keyassociated with a first asymmetric key pair; and one or more currentcertificate version numbers, each associated with a correspondingdigital certificate; wherein, in a secure boot process, the processor isconfigured to: load a digital certificate that includes a loadedcertificate version number associated with the digital certificate and asecondary public key associated with a second asymmetric key pair;authenticate the loaded digital certificate using the first public key;compare the loaded certificate version number with a correspondingcurrent certificate version number in the fuse-based memory, wherein theloaded certificate version number being equal to or higher than thecorresponding current certificate version number indicates that theloaded digital certificate is a trusted certificate; and determine thatthe loaded digital certificate is a trusted certificate; wherein theprocessor is further configured to replace a current certificate versionnumber stored in the fuse-based memory with the loaded certificateversion number associated with a trusted digital certificate, therebypreventing a digital certificate with an older certificate versionnumber from being determined as a trusted certificate.
 2. Thesystem-on-chip of claim 1, wherein, in the case that the loadedcertificate version number is higher than the current certificateversion number, the processor is further configured to update thecorresponding current certificate version number in the fuse-basedmemory with the loaded version number.
 3. The system-on-chip of claim 1,wherein the fuse-based memory also stores one or more current keyversion numbers, each associated with a corresponding secondary publickey; and wherein, after determining the loaded digital certificate to bea trusted certificate, the processor is further configured to: compare akey version number associated with the secondary public key of theloaded digital certificate with a corresponding current key versionnumber in the fuse-based memory; in the case that the key version numberis lower than the corresponding current key version number, determinethat the secondary public key is not a trusted public key; and in thecase that the key version number is equal to or higher than thecorresponding current key version number, determine that the secondarypublic key is a trusted public key.
 4. The system-on-chip of claim 3,wherein the processor is further configured to, in the case that the keyversion number is higher than the current key version number, update thecorresponding current key version number in the fuse-based memory toindicate the key version number of the secondary public key.
 5. Thesystem-on-chip of claim 1, wherein the processor is further configuredto, in the case that the loaded certificate version number is higherthan the current certificate version number, update the correspondingcurrent certificate version number in the fuse-based memory with theloaded certificate version number, in response to a command from atrusted entity.
 6. A computing device, comprising: a processor; apersistent memory for storing information about a first public keyassociated with a first asymmetric key pair for authenticating a digitalcertificate; and a second memory for storing one or more currentcertificate version indicators, each associated with a correspondingdigital certificate, wherein the one or more current certificate versionindicators are used by the processor to determine the trust of thecorresponding digital certificate; wherein the processor is furtherconfigured to: receive and authenticate a new trusted digitalcertificate to replace an old digital certificate that has beencompromised; and replace a current certificate version indicator storedin the second memory with a certificate version indicator of the newtrusted digital certificate, thereby preventing a digital certificatewith an older certificate version number from being determined as atrusted certificate.
 7. The computing device of claim 6, wherein theprocessor is configured to: load a digital certificate having a loadedcertificate version indicator; authenticate the loaded digitalcertificate using the first public key; compare the loaded certificateversion indicator with a corresponding current certificate versionindicator in the second memory; in the case that the loaded certificateversion indicator is lower than the current certificate versionindicator, determine that the loaded digital certificate is not atrusted certificate; and in the case that the loaded certificate versionindicator is equal to or higher than the current certificate versionindicator, determine that the loaded digital certificate is a trustedcertificate.
 8. The computing device of claim 7, wherein the processoris further configured to, in the case that the loaded certificateversion indicator is higher than the current certificate versionindicator, update the corresponding current certificate versionindicator in the second memory with the loaded certificate versionindicator.
 9. The computing device of claim 7, wherein the second memoryis further configured to store one or more current key versionindicators, each associated with a corresponding current secondarypublic key; and wherein the processor is further configured to, afterdetermining the loaded digital certificate to be a trusted certificate:compare a version indicator for a secondary public key provided by theloaded digital certificate with a corresponding current key versionindicator stored in the persistent memory; in the case that the versionindicator for the secondary public key is lower than the current keyversion indicator, determine that the secondary public key is not atrusted public key; and in the case that the version indicator for thesecondary public key is equal to or higher than the current key versionindicator, determine that the secondary public key is a trusted publickey.
 10. The computing device of claim 9, wherein the processor isfurther configured to, in the case that the version indicator for thesecondary public key is higher than the current key version indicator,update the corresponding current key version indicator in the persistentmemory to indicate the version indicator for the secondary public key.11. The computing device of claim 7, wherein the processor is furtherconfigured to, in the case that the loaded certificate version indicatoris higher than the current certificate version indicator, update thecorresponding current certificate version indicator in the persistentmemory with the loaded certificate version indicator, in response to acommand from a trusted entity.
 12. The computing device of claim 6,wherein, in the case that the loaded certificate version indicator ishigher than the current certificate version indicator, the processor isfurther configured to update the corresponding current certificateversion indicator in the second memory with the loaded certificateversion indicator, in response to a command from a trusted entity. 13.The computing device of claim 6, wherein the information about the firstpublic key comprises a symmetric key configured for decrypting anencrypted version of the first public key.
 14. The computing device ofclaim 6, wherein the information about the first public key comprisesprime numbers for deriving the first public key.
 15. The computingdevice of claim 6, wherein the persistent memory is a fuse-based memoryor a system boot ROM (read only memory).
 16. The computing device ofclaim 6, wherein the second memory is a fuse-based memory or is anelectrically erasable programmable non-volatile memory.
 17. A method forgenerating a digital certificate for a computing device, the computingdevice having a first public key associated with a first asymmetric keypair for authenticating a digital certificate, the method comprising:generating a second public key associated with a second asymmetric keypair and a corresponding key version number; generating a digitalcertificate including a certificate version number and the first publickey, the generated digital certificate further including the secondpublic key and the corresponding key version number associated with thesecond public key; signing the generated digital certificate; andsending the generated digital certificate to the computing device,wherein the computing device is configured to: authenticate thegenerated digital certificate using the first public key and thecertificate version number; extract the second public key and the keyversion number from the generated digital certificate; and authenticatethe second public key using the corresponding key version numberassociated with the second public key.
 18. The method of claim 17,wherein signing the generated digital certificate comprises: using ahash algorithm to generate a message digest of at least a portion of thegenerated digital certificate; encrypting the message digest using afirst private key associated with the first asymmetric key pair; andincluding the encrypted message digest in the generated digitalcertificate.
 19. The method of claim 17, wherein the certificate versionnumber associated with the generated digital certificate is higher thana certificate version number sent previously to the computing device.20. The method of claim 17, wherein the key version number associatedwith the secondary public key is higher than a public key version numbersent previously to the computing device.